1. Technical Field
The present invention relates to a semiconductor device and a method of manufacturing the semiconductor device.
2. Related Art
In recent years, as a material that constitutes a semiconductor device, utilization of a high-dielectric-constant film called high-k has been examined. Representative examples of a high-k material may include oxides including Zr and Hf. If these materials are used for a gate insulating film of a MOSFET, a high-speed transistor can be realized. Japanese Unexamined patent publication NO. 2002-280461 discloses a CMOS device that includes an nMOSFET and a pMOSFET using the high-k material.
Further, as a method of forming a metal gate, a gate-last (damascene gate) process that forms a gate electrode after forming a source/drain may be adopted. Japanese Unexamined patent publication NOs. 2007-134674, 2007-123551, 2002-270797, and 2002-184958 disclose structures of a metal gate. If this process is used, a metal material where patterning is difficult can be used as an electrode material.
The present inventor has recognized as follows. There is a type of transistor that constitutes for example a Dynamic Random Access Memory (DRAM). In such type of transistor, it may be preferable to maintain an excellent holding characteristic rather than the having high-speed characteristic. Therefore, in such type of transistor, it may be preferable to use a thick silicon oxide film as a gate dielectric film rather than using high-k dielectric film as a gate dielectric film.